There are a variety of application areas for WLANs. For example, there are cases where a user in a company normally uses a notebook computer on the desktop, but sometimes moves to a conference room or the like, or cases where an access point connected to a home AV server comprising a plurality of devices such as a set-top box, media player, Internet portal, or a display panel, camera, notebook computer, or the like equipped with a wireless access device, accesses media stored on the Internet or a home AV server. A WLAN can also be applied to a cellular hotspot in the lobby of an office building, a coffee shop, or the like, accessed by mobile users of data services.
IEEE802.11 (see Non-Patent Document 1) is a highly cost—effective solution that provides wireless connection of computers and other devices to a network. Through new developments in signal processing and modulation techniques, the standard has been extended to support a new physical layer at a higher data transfer rate (see Non-Patent Document 2 and Non-Patent Document 3). According to research, a major restriction of present 802.11 systems is the MAC (medium access control) layer, and as a result, saturation of throughput associated with increased data transfer rates occurs (see Non-Patent Document 4). The IEEE802.11 Working Group has confirmed the necessity of high-throughput WLANs based on MAC and PHY (physical layer) changes with respect to current WLANs (see Non-Patent Document 5). One important issue highlighted is the necessity of support/recognition of current systems (see Non-Patent Document 5 and Non-Patent Document 6).
Non-Patent Document 1 through Non-Patent Document 6 referred to here are as follows.
Non-Patent Document 1: “Local and Metropolitan Area Networks-Specific Requirements-Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications”, IEEE Std 802.11-1999, IEEE, August 1999
Non-Patent Document 2: “Local and Metropolitan Area Networks-Specific Requirements-Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: Higher-Speed Physical Layer Extension in the 2.4 GHz Band”, IEEE Std 802.11b-1999, IEEE, September 1999Non-Patent Document 3: “Local and Metropolitan Area Networks-Specific Requirements-Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: Higher-Speed Physical Layer Extension in the 5 GHz Band”, IEEE Std 802.11a-1999, IEEE, September 1999Non-Patent Document 4: Y. Xiao & J. Rosdahl, “Throughput Analysis for IEEE 802.11a Higher Data Rates”, doc.: IEEE 802.11/02-138r0, March 2002 Non-PatentDocument 5: J. Rosdahl et al, “Draft Project Allocation Request (PAR) for High-throughput Study Group”, doc.: IEEE 802.11/02-798r7, March 2003 Non-Patent Document 6: E. Perahia, A. Stephens, S. Coffey, “Backward Compatibility Case Studies”, doc.: IEEE 802.11-03/307r0, May 2003
Based on current applications and applications envisaged for the future, data transfer rates supported by existing WLANs are sufficient (see Non-Patent Document 7: J. del Prado, K. Challapali, S Shankar and P. Li, “Application Characteristics for HT Usage Scenarios”, doc.: IEEE 802.11-03/346r0, May 2003). As WLANs traditionally comprise time division multiple access devices, the number of high-speed data transfer application users that can be simultaneously supported by a network is a problem. This problem can be generalized as a problem of the need for higher throughput. A means of achieving higher throughput is to increase the data transfer rate measured in a higher layer than layer 2 based on the International Organization for Standardization (ISO) Open Systems Interconnection (OSI) model, or the medium access control layer. In order to satisfy the conditions necessary for increasing the total throughput of all wireless stations of one basic service set comprising a single wireless access point and a plurality of wireless stations, the throughput of a wireless LAN system is measured at an access point.
While increasing the RF spectrum used would be one solution, this is not an option. This is because the available spectrum is a limited resource, and has already been deployed for other applications. Also, due to the necessity for backward compatibility with current devices, new systems must conform to spectrum masking and already used channelization.